Serotonin: Brains, Bowels, Bones and Beyond

One of the fascinating aspects of medicine and biology is how one substance can have so many functions.  A recent article about the effects of serotonin on bone cells and bone formation in the New York Times illustrates this point. While this finding about serotonin and bone formation may be important for developing new ways to treat osteoporosis, it is especially fascinating because serotonin does so many other things in the body.

Serotonin is probably best known for how its levels affect mood – which is the basis for the medicines to treat depression in the class known as “Selective Serotonin Reuptake Inhibitors,” or SSRIs. Serotonin is also involved with the functioning of the gastrointestinal system – primarily as a neurotranmitter in the GI track’s nervous system effecting the peristaltic movement of the intestines. [Click here for a 2001 video from Novartis about serotonin and Irritable Bowel Syndrome.]

What the research article in Cell shows is that high levels of serotonin may inhibit bone formation as well. This understanding may be the basis for creating new treatments for osteoporosis – and is a new avenue for addressing this disease that hadn’t been considered before.  As the New York Times characterizes it, “Osteoporosis researcher were dumbfounded by the report.”

While this is very interesting in itself, as I stated at the start of this post, what is globally more enlightening is how one compound can have very different effects on the human body depending upon where it is found.  This is often seen in how medicines may have effects other than those they are intended to produce.  These are generally called “side-effects,” but really they may be seen as “other effects,” and sometimes they are used as the primary reason for using a medicine.  (To avoid giving what might seem like medical advice, I’ll refrain from listing specifics here, but would be interested if anyone has comments or insights into this.)

And of course, there are also the side-effects that turn out to be the primary effect for a new medicine.  Most famously, this is what led to the development of Viagra®, a medicine that was intended to promote blood flow in the arteries of the heart, but which actually caused increased blood flow elsewhere.

What this all means is that there are still many unknowns in biomedicine, and that many future discoveries will help us develop better treatments for many diseases by shifting our understanding of how the body works.  As I was told in a lecture on the first day of medical school, “Half of what we’re going to teach you is wrong – we just don’t know which half.”  I know that in the few/several/many years since I graduated medical school, biomedical research has discovered a tremendous amount of new knowledge about human health and disease.  But I also suspect that the percentage of what medical students are taught today which will need to be changed in the coming years hasn’t shifted very much, if at all, because more knowledge also leads to asking more questions – which, of course, are really the starting point for new discoveries that lead to better treatments…… and also require medical school professors to revise their lectures every year.

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